Metering system and method for supplying gas to a torch

ABSTRACT

A metering system and associated method for supplying gas to a torch are provided. The metering system includes a controller that is configured to adjust a pressure regulator according to the pressure and flow rate of the gas delivered to the torch. For example, the torch can be a plasma arc torch that has an electrode positioned in a nozzle and operates in a working mode by providing an arc from the electrode to a workpiece. In a first mode of operation, the metering system can provide a gas to the torch by adjusting the pressure regulator according to the pressure downstream of the pressure regulator. In a second mode of operation, the metering system can provide adjust the pressure regulator according to the flow rate of the gas through a flow transducer in series with the pressure regulator. Further, the metering system can be configured to monitor the downstream pressure and the flow rate of the gas and determine therefrom whether there exists in the torch a double arc or other operating condition that affects the flow of the gas through the nozzle.

BACKGROUND OF THE INVENTION

1) Field of the Invention

The invention relates to the supply of a gas to a torch such as a plasmaarc torch and, more particularly, to a system and method for controllingthe flow of the gas according to the operating parameters of the torch.

2) Description of Related Art

Plasma arc devices are commonly used for cutting and welding. Oneconventional plasma arc torch includes an electrode positioned within anozzle. A pressurized gas is supplied to the torch and flows through thenozzle and proximate to the torch, and an arc is established between theelectrode and a workpiece. For example, according to one typical methodfor starting the torch, a pilot mode is first initiated by establishingan arc at a low current between the electrode and the nozzle. A flow ofgas is also delivered through the nozzle during the pilot mode. Thetorch is then switched from the pilot mode to a transfer or working modeby transferring the arc to the workpiece so that the arc extends betweenthe electrode and the workpiece. The current of the arc is increased forthe working mode, and the flow rate or type of the gas can also beadjusted. The arc ionizes the gas, and the resulting high temperaturegas can be used for cutting or other welding operations. One such torchand a start-up operation are further described in U.S. Pat. No.5,017,752, titled “Plasma arc torch starting process having separatedgenerated flows of non-oxidizing and oxidizing gas,” issued May 21,1991, which is assigned to the assignee of the present invention and theentirety of which is incorporated herein by reference.

A metering system supplies the gas that flows through the nozzle of thetorch. One conventional metering system operates by attempting toprovide a constant pressure in the gas that is delivered to the torch.That is, the metering system is disposed between a source of the gas andthe torch and controls the flow of the gas from the source to the torchaccording to the pressure downstream of the metering system. Forexample, the metering system can be a mechanical pressure regulator or aproportional valve that receives a feedback signal indicative of thepressure of the gas flowing from the metering system to the torch.Constant pressure metering systems typically provide quick response.That is, the pressure can be changed relatively quickly at start-up orotherwise as desired. However, the flow rate provided by a constantpressure metering system can vary, thereby affecting the performance ofthe torch and possibly increasing wear on the components of the torch.

Another conventional metering system is configured to provide a constantflow rate of the gas to the torch. For example, a constant flow ratemetering system can include a throttle valve for controlling the flow ofthe gas from the gas source to the torch. If the throttle valve receivesthe gas at a constant upstream pressure from the gas source, and thedownstream pressure is sufficiently less than the upstream pressure, theflow through the throttle valve will be constant. Constant flow meteringcan also be achieved by providing a constant upstream pressure through aproportional valve or a fixed orifice. A bank of selectable orifices canbe provided so that different flow rates can be achieved duringdifferent modes of operation of the torch. Alternatively, a fixedorifice can selectively receive different upstream pressures accordingto the desired flow rate. In any case, constant flow metering generallyprovides consistent torch performance, and can also provide optimum lifeof the torch components. However, the time required to stabilize asystem with constant flow can be considerable. That is, although theflow rate may be constant through the metering system, the flow rate andpressure downstream in the torch may vary asymptotically duringtransient modes of operation, such as during start-up of the torch. Inparticular, after-the metering system begins to provide a constant flowof gas, the flow path for the gas between the metering system and thetorch may take 10 seconds or longer to achieve a stabilized pressure,during which time the torch may not operate efficiently.

Regardless of the type of metering system, the electrode can becomeeroded during operation. Erosion can be minimized, for example, bysupplying a non-oxidizing gas to the torch during certain modes ofoperation. However, the electrode can still be eroded, especially ifsubjected to stress, repeated starting and stopping, or the like. Inparticular, the electrode can deteriorate quickly if a double arcexists, i.e., if arcs simultaneously exist between the electrode and thenozzle and between the electrode and the workpiece.

Thus, there exists a need for an improved metering system and associatedmethod for providing gas to a torch. The system should be capable ofproviding the gas at a substantially constant flow rate. Additionally,the system should be capable of changing the flow rate at the torchrelatively quickly, such as at start-up of the torch or during othertimes when it is desirable to adjust the rate of flow according to theoperation of the torch. Further, the system should optionally providedetection of particular modes of operation of the torch that may beundesirable, such as the existence of double arcs.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a metering system and an associatedmethod for supplying gas to a torch, such as a plasma gas torch forcutting or other welding operations. The torch typically includes anelectrode positioned in a nozzle and delivers gas through the nozzle forionization by an electric arc during a working mode of the torch. Themetering system includes a pressure regulator and a controller that isconfigured to selectively adjust the pressure regulator according to aflow rate and a pressure of the gas delivered to the torch. Thus, thepressure regulator can be adjusted to quickly achieve a predetermineddownstream pressure and also to accurately achieve and maintain apredetermined flow rate.

According to one embodiment of the present invention, the meteringsystem includes a flow rate transducer, such as a mass flow rate meter,and a pressure transducer. The flow rate transducer is configured tomeasure a flow of the gas and provide a flow signal indicative of theflow rate of the gas to the torch. The pressure transducer is configuredto receive the flow of the gas and indicate the pressure of the gas. Acontroller communicates with the flow rate transducer and the pressuretransducer and adjusts the pressure regulator accordingly. For example,the controller can be configured to operate selectively in first andsecond modes. In the first mode, the controller adjusts the pressureregulator to provide a predetermined downstream pressure. In the secondmode, the controller adjusts the pressure regulator according to theflow rate of the gas to the torch, e.g., to maintain a predeterminedflow rate. The controller can receive electrical signals from the flowrate transducer and/or the pressure transducer and control the pressureregulator via a pressure signal or other fluid signal.

The system can also be configured to detect a geometric aspect or changein geometry of the torch by monitoring the flow of the gas through thetorch. For example, the controller can be configured to compare the flowsignal and the pressure of the flow to at least one predetermined valueand thereby detect a change in the geometry of the flow path of thetorch. Thus, the controller can detect an enlarged or restricted nozzleof the torch by detecting a flow rate therethrough that is higher orlower than a predetermined value for a particular operating pressure. Insome cases, the controller can respond to a change in the geometry ofthe torch by interrupting operation of the torch.

The present invention also provides a method of supplying a gas to aplasma torch. According to one embodiment, the method includes measuringa flow rate, such as a mass flow rate, and pressure of the gas flowingto the torch. A pressure regulator is adjusted according to the pressureof the gas supplied to the torch to substantially supply at least onepredetermined pressure. In addition, the pressure regulator is adjustedaccording to the flow rate of the gas to provide a substantially steadyflow rate of the gas to the torch. For example, a first predeterminedpressure can be provided during starting of the torch, and a secondpredetermined pressure, which can be higher or lower than the firstpredetermined pressure, can be provided after an arc is established inthe torch. Thereafter, the pressure regulator can be adjusted accordingto the flow rate to maintain a steady flow rate.

In addition, a geometric aspect of the torch can be detected bycomparing the flow rate and the pressure of the flow to at least onepredetermined value. For example, an enlarged nozzle orifice can bedetected if the flow rate through the torch is larger than thepredetermined value for a particular pressure in the torch or if thepressure of the gas flowing through the torch is less than apredetermined value. A double arc detection signal can be issued inresponse to detection of such enlargement, and/or an operation of thetorch can be automatically interrupted.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

Having thus described the invention in general terms, reference will nowbe made to the accompanying drawings, which are not necessarily drawn toscale, and wherein:

FIG. 1 is a schematic diagram illustrating a plasma arc cuttingapparatus including a metering system for a torch according to oneembodiment of the present invention; and

FIG. 2 is a schematic diagram illustrating a metering system accordingto one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which some, but not allembodiments of the invention are shown. Indeed, this invention may beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided so that this disclosure will satisfy applicable legalrequirements. Like numbers refer to like elements throughout.

Referring now to the drawings, and in particular to FIG. 1, there isschematically illustrated a plasma arc cutting apparatus 10 including ametering system 50 according to one embodiment of the present invention.The metering system 50 controls the flow of one or more gases that flowfrom gas sources 12 a-12 f to a torch 14. Typically, the torch 14 is aplasma arc torch, which can be used for cutting or other weldingoperations. Generally, the torch 14 includes an electrode 16 positionedin a nozzle 18. An arc can be established between the electrode 16 and aworkpiece 20 (or between the electrode 16 and the nozzle 18, such asduring the pilot mode), and a flow of gas is provided through the nozzle18 to be ionized by the arc during the cutting process. The flow of gasto be ionized during operation of the torch 14 is received by the torch14 via a plasma gas inlet 22 that is fluidly connected to the meteringsystem 50. In addition, the torch 14 defines a shield gas inlet 24configured to receive a shield gas that is circulated in the torch 14 ina flow path adjacent to the electrode 16 and generally radially outsidethe flow of plasma gas. The structure and operation of plasma arctorches are further described in U.S. Pat. No. 6,215,090, titled “Plasmaarc torch,” issued Apr. 10, 2001 and U.S. application Ser. No.10/294,968, titled “Plasma Arc Torch and Method of Operation,” filedNov. 14, 2002, each of which is assigned to the assignee of the presentinvention, and the entirety of each of which is incorporated herein byreference. An electrode for a plasma arc torch is described in U.S. Pat.No. 5,023,425, titled “Electrode for plasma arc torch and method offabricating same,” issued Jun. 11, 1991, the entirety of which is hereinincorporated by reference. It is appreciated that the metering system 50of the present invention can be used with a variety of torches and canbe used to control various types of gases.

Multiple gases can be supplied to the torch 14 for different uses in thetorch 14 or 10 during the different operations of the torch 14. Forexample, as shown in FIG. 1, while the metering system 50 is configuredto meter a flow of plasma gas for a cutting operation through a cutplasma gas line 26, the system 50 can also supply a start plasma gasthrough a start plasma gas line 28, a cut shield gas through a cutshield gas line 30, a start shield gas through a start shield gas line32, and an air curtain gas from an air source via air line 34. The flowof air through air line 34 can be provided by an air source 36 andcontrolled by a solenoid 38. In some cases, a flow of water is suppliedto the start shield gas line 32 instead of the shield gas. The water canbe supplied from a water supply source 40 via a water pump 42, whichincludes a pump 44, a solenoid 46 and a flow transducer 48. A checkvalve 49 can be provided between the source 40 and the start shield gasline 32.

Each gas supplied for the cutting or other operation can be a mixturecomprised of multiple component gases, which can be selected accordingto the type and operation of the torch 14. For example, as shown in FIG.1, the gases delivered to the torch 14 can be delivered as a mixture ofoxygen, hydrogen, methane, nitrogen, argon, and air, each of which issupplied by a respective gas source 12 a-12 f. Each of the sources 12a-12 f can be a pressure vessel or other device for supplying therespective gas. Further, each source 12 a-12 f can supply the respectivegas at a predetermined and constant pressure. In this regard, eachsource 12 a-12 f can include a pressure regulator or pressure adjustmentdevice for limiting or otherwise controlling the pressure of the gassupplied to the 30 metering system 50.

The plasma and shield gases used in the torch 14 generally flow from thegas sources 12 a-12 f, through the gas metering system 50, to a torchmanifold 80, and therethrough to the torch 14. The metering system 50includes an inlet manifold 52, which includes a number of check valves54 a-54 f and solenoids 56 a-56 f, 58 a-58 d, 59 a-59 b for controllingthe direction of flow and for starting and stopping the flow from thesources 12 a-12 f. That is, each gas entering the inlet manifold 52flows through the respective check valve 54 a-54 f to the respectivesolenoid(s) 56 a-56 f, 58 a-58 d, 59 a. Multiple solenoids can beprovided for each gas to separately control the flow of the gas throughthe gas lines 26, 28, 30, 32 to the torch 14. For example, the solenoids56 d, 58 d control the flow of the oxygen from oxygen source 12 d. Byopening and closing the solenoid 56 d, a flow of the oxygen to a mixregulator 60 can be controlled. A flow of the oxygen to the cut plasmagas line 26 can separately be controlled by opening and closing thesolenoid 58 d. Similarly, solenoids 56 e, 56 f control the flow of thehydrogen and methane to the mix regulator 60, respectively, andsolenoids 56 a-56 c, 58 a-58 c separately control the flows of nitrogen,argon, and air to a shield regulator 62 and the cut plasma gas line 26,respectively. Solenoid 59 a controls the flow of nitrogen to the startplasma gas line 28, and solenoid 59 b selects the gas selected as thecut plasma gas for the start plasma gas line 28. Filters 64 a, 64 b canbe provided throughout the metering system 50, and pressure transducers66 a, 66 b can be provided for detecting the pressure of the gases indifferent portions of the system 50. For example, the pressuretransducers 66 a, 66 b can detect the pressure of the gases entering themix regulator 60 and the shield regulator 62, and the pressuretransducers 66 a, 66 b can display the pressures to an operator and/ormonitor the pressures to warn an operator or interrupt an operation ofthe apparatus 10 if the pressures fall below a minimum value or exceed amaximum value.

The mix and shield regulators 60, 62 can be flow regulation devices thatare configured to maintain a substantially constant flow ratetherethrough. For example, each regulator 60, 62 can include a pluralityof parallel orifices that are selectively disposed in the path of flowaccording to the desired flow rate. From the regulators 60, 62, thegases flow to a check valve and solenoid manifold 70, i.e., anarrangement of solenoids 72 a-72 c and check valves 74 a-74 d configuredto control the flow of the gases to the torch manifold 80. Thus, the mixregulator 60 acts as a shield regulator when the solenoid 72 b is open.The torch manifold 80, in turn, includes check valves 82 a-82 c andsolenoids 84 a-84 d for selectively connecting the cut plasma gas line26 and start plasma gas line 28 to the plasma gas inlet 22 of the torch14 and for selectively connecting the cut shield gas line 30 and startshield gas line 32 to the shield gas inlet 24.

Therefore, the supply of the plasma gas to the plasma gas inlet 22 ofthe torch 14 is provided via the cut plasma gas line 26 and the startplasma gas line 28. In particular, solenoid 59 a can be selectivelyopened and closed to control the flow of nitrogen to the start plasmagas line 28. The nitrogen flows from the solenoid 59 a to a pressureregulator 90, which can be adjusted according to a pressure downstreamof the regulator 90. That is, the pressure regulator 90 can be a valve,such as a proportional valve, or another device and can include apressure feedback loop that is internal or external to the pressureregulator 90. For example, a pressure setting device 92 can beconfigured to receive an electrical pressure signal from a pressuretransducer 94 indicative of the downstream pressure at the transducer94. The pressure transducer 94 can be a pressure gauging deviceconfigured to measure a pressure and provide an electrical signalindicative of the measured pressure. The pressure setting device 92 canadjust the pressure regulator 90 accordingly, e.g., by opening orclosing the regulator 90 in response to the measured pressure to achievea predetermined pressure at the pressure transducer 94. For example, thepressure setting device 92 can be an electromechanical device such as anelectronically controlled pressure setting device that receives anelectric pressure signal from the pressure transducer 94 or a controllerand adjusts the pressure regulator 90 by adjusting a fluid controlpressure delivered through a control line 96 to the pressure regulator90. The control pressure can be provided by one of the pressure sources,such as the nitrogen source 12 a through pressure supply line 98 asshown in FIG. 1. The gas flows from the pressure regulator 90 via thecheck valve 82 a in the torch manifold 80 to the plasma gas inlet 22 ofthe torch 14. The solenoid 84 a in the torch manifold 80 can also beused to selectively vent some or all of the gas flowing through thestart plasma gas line 28.

Gases flowing to the cut plasma gas line 26, such as nitrogen, argon,air, and oxygen, can be supplied through the respective solenoids 58a-58 d. Some or all of the gas flowing through the solenoids 58 a-58 dcan be directed through the solenoid 59 b to the start plasma gas line28 so that the start plasma gas can be the same as the cut plasma gas.Otherwise, the gas flows to a pressure switch 100 and a fixed pressureregulator 102, which can be configured to provide a predeterminedpressure, such as about 100 psi. Thereafter, the gas is directed througha mass flow transducer 104, through an adjustable pressure regulator106, and to a pressure transducer 108. Similar to the pressure regulator90 in the start plasma gas line 28, the pressure regulator 106 can beadjusted by a pressure setting device 110. That is, the pressure settingdevice 110 can be configured to receive a pressure signal from thepressure transducer 108 indicative of the downstream pressure in the cutplasma gas line 26 and adjust the pressure regulator 106 accordingly,e.g., by controlling a control pressure in a control line 112. Thus, thepressure setting device 110 and the pressure regulator 106 can maintaina predetermined pressure in the cut plasma gas line 26, substantiallyregardless of flow variations in the torch 14 that might otherwiseaffect the pressure in the cut plasma gas line 26. The cut plasma gasline 26 can also be configured to receive a flow of gas from the checkvalve and solenoid manifold 70, i.e., via the solenoid 72 a and checkvalve 74 a. A “T” fitting 142 or fluid chamber is provided in the cutplasma gas line 26 so that the gases entering the line 26 are mixedtherein. The check valve 82 b and solenoid 84 b in the torch manifold 80control the delivery of the gas into the plasma gas inlet 22 of thetorch 14.

The pressure regulator 106 can be responsive to the mass flow ratetransducer 104 in addition to the downstream pressure transducer 108. Inthis regard, there is illustrated in FIG. 2 a controller 120 configuredto communicate with the pressure transducer 108 and the mass flow ratetransducer 104 and control the pressure regulator 106 accordingly. Thecontroller 120 can include a processor 122 that operates according topredetermined operating instructions, such as programmable software codestored in a memory 124. In particular, the mass flow rate transducer 104can be configured to measure a mass flow rate of the gas flowingtherethrough, and the pressure transducer 108 can be configured todetect the pressure of the gas flowing downstream of the pressureregulator 106. The mass flow rate transducer 104 can be anelectromechanical device that generates an electrical flow signal thatis proportional to the mass flow rate. For example, the mass flow ratetransducer 104 can measure the electrical characteristics of aconductive wire disposed in the flow path of the cut plasma gas line 26and provide an electrical flow signal based thereon. While the mass flowtransducer 104 is illustrated as receiving all of the gas flowingthrough the cut plasma gas line 26, the mass flow transducer 104 caninstead be configured to measure the flow rate by monitoring only aportion of the gas flowing through the line 26, and in some cases, themass flow transducer 104 does not receive the gas or receives only aportion of the gas being measured. Further, while the mass flowtransducer 104 is illustrated as being upstream of the pressureregulator 106 in FIG. 2, it is appreciated that the mass flow transducer104 can be positioned elsewhere in the apparatus 10, such as downstreamof the pressure regulator 106. The mass flow rate transducer 104 and thepressure transducer 108 can communicate signals indicative of the massflow rate and the downstream pressure to the controller 120. Thecontroller 120, in turn, can receive the signals from the mass flow ratetransducer 104 and the pressure transducer 108 and respond by adjustingthe pressure setting device 110, which accordingly adjusts pressureregulator 106.

The controller 120 can be configured to operate in multiple modes ofoperation. In each mode, the controller 120 can control the pressureregulator 106 by adjusting the pressure setting device 110. That is, thecontroller 120 need not communicate directly with the pressure regulator106 to control the regulator 106. In a first exemplary mode ofoperation, the controller 120 can adjust the pressure regulator 106according to the pressure transducer 108. In a second mode of operation,the controller 120 can adjust the pressure regulator 106 according tothe mass flow rate transducer 104. In particular, in the first mode, thecontroller 120 can be programmed to regulate the pressure regulator 106to achieve a predetermined downstream target pressure at the pressuretransducer 108. The controller 120 can generally do so by opening thepressure regulator 106 if the downstream pressure is lower than thetarget pressure and closing the pressure regulator 106 if the downstreampressure is greater than the target pressure. The controller 120 canadjust the pressure regulator 106 to varying degrees according to thedifference between the target pressure and the downstream pressure oraccording to a characteristic of either of those pressures, such as therate of change of the pressures. Further, in some cases, the controller120 can adjust the pressure regulator 106 according to predeterminedparameters for achieving a particular pressure. For example, thecontroller 120 can be programmed with an adjustment setting for thepressure regulator 106 that corresponds to a predetermined targetpressure. Thus, when adjusting the pressure regulator 106 to achieve andmaintain the programmed target pressure, the controller 120 can adjustthe pressure regulator 106 to the programmed setting and, optionally,perform additional adjustment to the pressure regulator 106 thereafter.

In addition, the controller 120 can adjust the pressure regulator 106 toachieve different target pressures according to the operation of thetorch 14. For example, during starting of the torch 14, the controller120 can first adjust the pressure regulator 106 to achieve a firststeady state pressure that is associated with a flow rate that has beenpreviously determined to be appropriate for starting of the torch 14.Then, after the arc is established, the controller 120 can adjust thepressure regulator 106 to achieve a second pressure that is associatedwith a flow rate that is appropriate for operating the torch 14 in acutting mode. For example, the flow of gas through the plasma chambercan be affected by the temperature of the gas in the plasma chamber whenthe arc is initiated, which in turn affects the pressure of the gasnecessary upstream of the plasma chamber to achieve a certain flow rate.The required pressures for achieving particular rates of flow can bedetermined theoretically or empirically and stored in the memory 124. Inthis way, the controller 120 can adjust the pressure regulator 106 toquickly achieve a substantially steady downstream pressure thatcorresponds to a flow rate appropriate for each operating mode of thetorch 14. Even if the flow path of the gas downstream of the pressureregulator 106 defines a large volume, e.g., if a long gas hose isdisposed between the pressure regulator 106 and the torch 14, thecontroller 120 can quickly achieve an appropriate flow rate at the torch14 by adjusting the pressure regulator 106 according to the downstreampressure. Thus, the controller 120 can quickly achieve a substantiallysteady state operation.

In the second mode of operation, the controller 120 can instead adjustthe pressure regulator 106 according to the mass flow rate as measuredby the mass flow rate transducer 104. That is, the controller 120 canreceive the signal from the mass flow rate transducer 104 indicative ofthe mass flow rate therethrough and adjust the pressure regulator 106 toincrease or decrease the flow rate in order to achieve a target flowrate. For example, after the arc is established and the controller 120has adjusted the pressure regulator to substantially achieve a targetdownstream pressure, the controller 120 can automatically enter thesecond mode of operation and begin adjusting the pressure regulator 106,e.g., “fine tuning” the pressure regulator 106 to substantially achievethe target flow rate. Although adjustment of the pressure regulator 106according to the flow rate can be slower to achieve steady stateoperation, adjustment according to the flow rate can be used after asubstantially steady state is achieved to thereafter more accuratelyprovide a steady flow rate of the gas to the torch 14. An accuratelycontrolled flow rate of gasses is considered to be important forachieving improved steady-state torch operation and life. Thus, after anappropriate flow rate is substantially achieved according to thedownstream pressure in the first mode, the metering system 50 canthereafter continue to fine tune the flow rate to achieve and maintain asubstantially steady flow rate during operation of the torch 14.

The metering system 50 can be operated in successive modes of operationduring any transient state of operation of the apparatus 10. That is,the metering system can quickly achieve and maintain a desired rate offlow at any time during the operation of the torch by first adjustingthe pressure regulator 106 according to the downstream pressure and thenaccording to the flow rate. Transient states of operations can occur atstart-up, shut-down, or upon any structural or operational change of thetorch, gas sources 12 a-12 f, and the like. Further, while thecontroller 120 of FIG. 2 is illustrated as being configured forcontrolling the flow of the gas through the plasma cut gas line 26, itis appreciated that a controller 120 can alternatively, or additionally,be provided for controlling the plasma start gas, the shield gas, thewater from supply source 40, or other fluids to be used with the torch14 or otherwise.

In one embodiment of the present invention, changes in the flow of thegas through the torch 14 can be detected by monitoring changes in thepressure measured by the pressure transducer 108 or mass flow ratetransducer 104. For example, after the arc is established for a cuttingoperation with the torch 14, the controller 120 can be configured tocontinuously adjust the pressure regulator 106 according to the massflow rate measured by the mass flow rate transducer 104, as describedabove. In addition, the controller 120 can continuously mass flow rate,the downstream pressure at the pressure transducer 108, and/or therelationship of the mass flow rate of the gas to the torch 14 to thedownstream pressure. For example, the controller 120 can compare therelationship between the mass flow rate and the downstream pressure to apredetermined relationship for a particular type of torch and nozzle andthe particular operating parameters. The relationship can correspond toa geometric aspect of the torch 14, such as the size of the orifice ofthe nozzle 18. Thus, if the controller 120 detects an unexpectedrelationship between the mass flow rate and downstream pressure, thecontroller 120 can signal the operator with a warning light, sound, orthe like. Alternatively, the controller 120 can automatically interruptor terminate an operation of the torch 14, e.g., by terminating the arcand/or adjusting the gas flow.

In particular, the controller 120 can detect a change in the geometry ofthe torch 14, such as a change in the geometry of the nozzle 18 due toerosion or deterioration of the nozzle 18. For example, significanterosion of the nozzle 18 can be indicative of the occurrence of doublearcing in the torch 14. That is, if arcs simultaneously occur betweenthe electrode 16 and the nozzle 18 and between the electrode 16 and theworkpiece 20 during operation of the torch 14, the nozzle 18 can bequickly eroded, thereby enlarging the orifice of the nozzle 18. Suchenlargement of the nozzle orifice by double arcing, nicking or otherdamage to the nozzle 18, and the like can result in a higher thanexpected flow through the nozzle 18 for the same or lower pressures ofgases delivered to the torch 14. Alternatively, a lower than expectedflow for the same or higher pressure can indicate that the nozzle 18 isat least partially blocked, e.g., by debris disposed in the nozzle 18.Thus, a higher than expected flow for a particular pressure can indicateenlargement of the nozzle 18, while lower flow for a particular pressurecan indicate blockage. Thus, by monitoring the mass flow rate and thedownstream pressure, and comparing the relationship between the flowrate and pressure to expected values therefor, the controller 120 canaccurately detect the occurrence of double arcing or other undesirableconditions occurring in the torch 14. In some cases, the detection bythe controller 120 of double arcs or other problems can occur only afterthe nozzle 18 has been substantially affected. Nevertheless, suchmonitoring can prevent further damage from occurring to the apparatus 10after the nozzle 18 is damaged.

Many modifications and other embodiments of the invention set forthherein will come to mind to one skilled in the art to which thisinvention pertains having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it is tobe understood that the invention is not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

1. A metering system for supplying a gas to a plasma torch, the systemcomprising: a flow rate transducer configured to measure a flow rate ofthe gas and provide a flow signal indicative of a flow of the gas; apressure regulator in a series configuration with the flow ratetransducer, the pressure regulator being configured to receive the flowof the gas and control a pressure of the gas flowing to the torch; and acontroller configured to receive the flow signal from the flow ratetransducer and detect a pressure of the gas flowing from the pressureregulator to the torch, wherein the controller is configured to operateselectively in first and second modes, the controller in the first modebeing configured to adjust the pressure regulator according to thepressure of the gas flowing to the torch, and the controller in thesecond mode being configured to adjust the pressure regulator accordingto the flow rate of the gas to the torch.
 2. A system according to claim1 wherein in the first mode the controller is configured to adjust thepressure regulator to provide a predetermined pressure in the flow ofthe gas to the torch.
 3. A system according to claim 1 wherein the flowrate transducer is configured to provide the flow signal indicative ofthe mass flow rate of the flow of the gas to the torch, and wherein inthe second mode the controller is configured to adjust the pressureregulator to provide a substantially constant mass flow rate of the gasto the torch.
 4. A system according to claim 1 further comprising apressure transducer in fluid communication with the flow of the gas fromthe pressure regulator and configured to indicate the pressure of thegas to the controller.
 5. A system according to claim 4 wherein thepressure regulator is configured to receive the gas from the flow ratetransducer and deliver the gas to the torch.
 6. A system according toclaim 1 further comprising a pressure setting device configured toreceive an electrical signal from the controller and provide acorresponding fluid signal to the pressure regulator to adjust thepressure regulator.
 7. A system according to claim 1 wherein thecontroller is configured to detect a change in the flow of the gasindicative of a change in the geometry of the torch.
 8. A systemaccording to claim 1 wherein the pressure regulator is a proportionalvalve with a pressure feedback loop.
 9. A metering system for supplyinga gas to a plasma torch, the system comprising: a flow rate transducerconfigured to measure a flow rate of the gas and provide a flow signalindicative of a flow of the gas; a pressure transducer configured toprovide a pressure signal indicative of the pressure of the gas; and acontroller configured to receive the flow signal from the flow ratetransducer and detect a pressure of the gas flowing from the pressureregulator to the torch, wherein the controller is configured to comparethe flow signal and the pressure of the gas to at least onepredetermined value and thereby detect a geometric aspect of the torch.10. A system according to claim 9 wherein the controller is configuredto detect a flow rate through the torch that is larger than apredetermined value, thereby detecting an enlarged nozzle orificedefining a portion of a flow path of the torch.
 11. A system accordingto claim 9 wherein the controller is configured to detect a pressure ofthe gas that is less than a predetermined value, thereby detecting anenlarged nozzle orifice defining a portion of a flow path of the torch.12. A system according to claim 9 wherein the controller is configuredto automatically interrupt an operation of the torch upon detection ofthe geometric aspect of the torch.
 13. A method of supplying a gas to aplasma torch, the method comprising: measuring a flow rate of the gasflowing to the torch; measuring the pressure of the gas flowing to thetorch; adjusting a pressure regulator according to the pressure of thegas supplied to the torch to substantially supply at least onepredetermined pressure; and adjusting the pressure regulator accordingto the flow rate of the gas to substantially supply at least onepredetermined flow rate of the gas to the torch.
 14. A method accordingto claim 13 wherein said first measuring step comprises measuring themass flow rate of the gas flowing to the torch.
 15. A method accordingto claim 13 wherein said adjusting steps comprise controlling thepressure regulator with a controller configured to detect the mass flowrate and the pressure of the gas supplied to the torch.
 16. A methodaccording to claim 13 wherein said adjusting steps comprisecommunicating an electric signal to control the pressure regulator. 17.A method according to claim 16 wherein said adjusting steps comprisecommunicating the electric signal to a pressure setting device such thatthe pressure setting device provides a corresponding fluid signal to thepressure regulator for adjusting the pressure regulator.
 18. A methodaccording to claim 13 wherein said first adjusting step comprisesproviding a first predetermined pressure during starting of the torch,and providing a second predetermined pressure after an arc isestablished in the torch, the second predetermined pressure beingdifferent than the first predetermined pressure, and wherein said secondadjusting step comprises controlling the pressure regulator after saidfirst adjusting step.
 19. A method according to claim 18, furthercomprising determining at least one of the first and secondpredetermined pressures according to a desired flow rate of the gasthrough the torch.
 20. A method according to claim 13, furthercomprising detecting a change in a flow of the gas indicative of achange in the geometry of the torch and responding to the change byissuing a double arc detection signal.
 21. A method according to claim20, further comprising automatically interrupting an operation of thetorch upon detection of the change in the flow of the gas.
 22. A methodof supplying a gas to a flow path of a plasma torch, the methodcomprising: measuring a flow rate of the gas to the torch; measuring thepressure of the gas flowing to the torch; and comparing the flow rateand the pressure of the gas to at least one predetermined value andthereby detecting a geometric aspect of the flow path of the torch. 23.A method according to claim 22 wherein said measuring step comprisesmeasuring the mass flow rate of the gas flowing to the torch.
 24. Amethod according to claim 22, further comprising detecting a flow ratethrough the torch that is larger than the predetermined value, therebydetecting an enlarged nozzle orifice defining a portion of the flow pathof the torch.
 25. A method according to claim 22, further comprisingautomatically interrupting an operation of the torch upon detection ofthe geometry aspect of the flow path.